1. Field of the Invention
The present invention relates to a vehicle and a method for operating an engine in a vehicle.
2. Background Art
In an effort to reduce tail pipe emissions from vehicles, a variety of vehicle systems have, over the years, been modified and improved. For example, the ignition timing in a spark ignition engine may be adjusted based on various vehicle conditions to provide efficient combustion and reduced tail pipe emissions. Similarly, the timing of fuel injected into the cylinders in a diesel engine can also be controlled in an attempt to optimize combustion and reduce tail pipe emissions. In addition, the air-to-fuel ratio (A/F), and in particular the amount of fuel provided to the engine, may be controlled to reduce tail pipe emissions.
Controlling the A/F can be accomplished using a closed loop control system, such that after the air/fuel mixture is combusted, the exhaust gases are analyzed to determine adjustments to the A/F. Japanese Patent No. JP1313641 describes a system that uses an oxygen sensor to sense the O2 concentration in the exhaust gas, and then uses this information as a feedback to control the A/F. One limitation of such a closed loop system is that it may not provide accurate information immediately following engine startup. Thus, until the engine has run for a certain amount of time and/or has achieved a certain temperature, it may be necessary to control the A/F with an open loop system. As used in this context, an open loop system is one that does not analyze the exhaust gases as part of a feedback control to adjust the A/F on the front end.
One alternative to using a closed loop system to control the A/F is to use one or more engine parameters that can be determined even if the engine is cold and/or in a transient startup state. For example, the engine speed, as measured by the crankshaft angle over time, may be used to help control the A/F for the engine. In a conventional vehicle, crankshaft position measurements may be one of only a few ways to determine the output of an engine, and thereby provide some basis for controlling the A/F for the engine. In non-conventional vehicles, however, such as hybrid electric vehicles (HEV), measuring the engine crankshaft angle over time may not be necessary to determine the engine output. Moreover, it does not take advantage of the interaction between the engine and an electric machine, such as a generator or a motor, which is a hallmark of HEV's.
Therefore, a need exists for a method for operating an engine in a hybrid electric vehicle to improve engine performance and reduce emissions, wherein the method utilizes the interaction between the engine and an electric machine in the vehicle.